8.3 Coral reefs Flashcards
What is the importance of coral reefs?
- Seafood: yield up to 15 tons of fish/other seafood per km squared
- estimated can provide food for up to a billion people in Asia alone
- Tourism: snorkelling/scuba diving is especially popular in the Red Sea
- much needed income in LICs
- Medical products: in rainforest some of the organisms living in the reef produce chemicals that can be used to cure disease, potentially including skin cancer and some viral diseases
- Coastal protection: coral reefs protect coastline from storm waves and can even break the power of tsunami waves
- especially important in areas where storms likely
- jewellery
What are the different types of coral reefs?
fringing reefs: grow near coastline around island/continents. Most common type.
barrier reefs: parallel to coastline, but separated by deep wide lagoons. At their shallowest points, they can reach water’s surface forming a “barrier” to navigation
atolls: rings of coral that create protected lagoons and are usually located in middle of the sea. Usually form when islands surrounded by fringing reefs sink into the sea/sea levels rises around them.
What are the conditions needed for coral growth?
Light:
- cannot grow in the water deeper than 30m as need sunlight to photosynthesise
- corals feed on plankton, need sunlight
Wave action:
- sufficient wave action which oxygenates the water so that the coral polyps can respire
- but too strong wave action can damage the structure of the calcium carbonate skeletons and risk erosion occurring increasing sediment levels
Salinity:
- grow best where salt levels are high
- prefer seawater with salinity levels between 32 and 42 psu
Sea bed:
- has to be solid surface which reef can grow on
- so form in shallow offshore waters
Sediment:
- polyps need Clean, clear, sunlit water so can’t live where rivers bring muddy sediments into sea and also need sediment clogs up feeding systems of coral polyps
Exposure to air:
- can’t survive for long above the water, so most of the reef is at or below low tide level
Temperature:
- must be above 18 degrees
- grow best where sea surface temp between 23 and 25 degrees why most are found between 30 degrees north and south of the equator
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What is the characteristics of an Atoll?
- Shape: ring-shaped coral reef enclosing a lagoon
- Lagoon: central lagoon, often relatively shallow
- Biodiversity: high biodiversity, with a variety of coral species, fish and other marine life
How do Atolls form?
- atolls consist of a ring shaped piece of coral situated away from the shore with a deep central lagoon
1. Volcanic island forms and a reef starts to grow around the island parallel to the coastline, forming a fringing reef
2. Island then begins to subside; it sinks due to rising sea levels or plate tectonics
3. This forms a central lagoon up to 50 meters deep and the reef separates fro the island forming a barrier reef
4. Complete submergence of the island then occurs but the coral reef continues to grow upwards as it has increased input available and the central lagoon becomes deeper - atoll
What is the distribution of atolls?
Geographic distribution: found in pacific/indian oceans
Pacific ocean: e.g Caroline, Marshall and Tuamotu archipelagos
Indian Ocean: Maldives
What are the characteristics of Fringing Reefs?
Proximity to shore: directly attached to the shore with no significant lagoon between reef/land
- Slope: gentle slope on shoreward side and steeper slope on seaward side
- Biodiversity: diverse
- Water depth: shallow water
How do fringing reefs form?
- Coral polyp settlement: coral larvae settle on submerged rocks/hard surfaces in shallow waters
- Growth and colonisation: these larvae develop into coral polyps, which beging to grow to form colonies. As they thrive, they secrete calcium carbonate, creating hard skeleton that contributes to the reef strucutr
- Expansion: as more polyps settle and grow, reef expands outward from the shore
What is the distribution of fringing reefs?
- Tropics: found where water temps suitable
- Caribbean: Bahamas
- Red sea: coastlines of Egypt
- Pacific oceans: coastline of Australia
What are the characteristics of barrier reefs?
- distance from shore: separated from mainland by wide, deep lagoon
- Lagoon: several km wide and vary in depth
- size: larger/more continuous than fringing reefs, stretching hundreds of km
- biodiversity: high
What is the formation of barrier reefs?
- Initial fringing reef stage: start forming adjacent to the coast
- subsidence and separation: as land/island subsides lagoon forms between the reef and the shore
- reef growth: coral continues to grow upwards/outwards, maintaining its position near the surface as land subsides
What is the distribution of barrier reefs?
- Great barrier Reef: Queensland, Australia
- Belize barrier Reef: coast of Caribbean sea
- New Caledonia Barrier Reef: southwest pacific ocean
How does global warming threat coral reefs and impacts?
Threat:
- coral bleaching occurs when ocean temps too high for algae to survive in corals
- more diseases and invasive species may thrive in warmer waters potentially harming corals
- more frequent, strong storms can disrupt/destroy coral reefs
- higher levels of CO2 lead to acidification, decreases growth rate
Impacts:
Environmental:
- bleaching kills coral = loss of diversity/habitat
Social:
- loss of jobs due to decrease in tourism
- families may struggle who rely heavily on resources from ocean
- 50% drugs made for humans derived some way from nature
Economic:
- loss of tourist will occur if coral becomes unattractive = loss of GDP for gov who rely on it
How does sea level rise threat coral reefs and what are its impacts?
Threat:
- increase in temperature = glaciers/ice sheets melting = rise in sea level
- if sea levels rise faster than upward growth of coral, may be too deep to receive sufficient sunlight
- rise in sea levels can cause increased coastal erosion, so more sediment is transported to the oceans, can lead to sedimentation in coral reefs, blocking sunlight
- especially in fringing reefs as close to shoreline
How does El Nino threaten coral reefs ?
Threat:
- El Nino is a climate pattern that causes unusual warming of surface waters in the eastern Pacific Ocean
- may raise chances of coral bleaching across Great Barrier Reef
- during 2015-2016 even experienced prolonged periods of elevated sea temps